1. Field of the Invention
The present invention relates to gas-operated firearms and, more particularly, to an improved bolt and bolt carrier for use in such firearms.
2. Description of the Related Art
The AR15/M16 family of weapons and their derivatives, including all direct gas operated versions, have been in use by the military and civilian population for many years. An essential part of this firearm's design is the bolt carrier which typically includes a bolt mounted in the carrier for axial sliding movement and rotation, a firing pin slidably mounted within the bolt and bolt carrier for restricted reciprocating axial movement, and a cam pin for producing relative rotation between the bolt and the bolt carrier.
The bolt carrier is generally cylindrical in shape with a longitudinally extending circular bore throughout its length. An elongated opening is provided in the top and bottom of the carrier to allow the hammer to extend into the interior of the bolt carrier and strike the firing pin. The rear of the carrier is received within the firearm receiver and the front of the carrier houses the bolt. The upper surface of the carrier immediately adjacent the front face includes a flat shelf for engagement with a charging handle. About the exterior of the bolt carrier are a series of lands and accompanying grooves, usually four, which extend from the forward end of the bolt carrier rearwardly over a distance of about one half the length of the bolt carrier. There are openings on the bolt carrier to mount a gas key, an opening which serves as a gas receiving port and an opening to receive the cam pin. Typically the gas key is secured to the bolt carrier through the use of two screws while the firing pin is retained in place through the use of a retaining or cotter pin.
Like the bolt carrier, the bolt has a body that is generally cylindrical in shape and is provided with a circular bore throughout its length which is designed to accommodate a firing pin. Located radially about a forward portion of the bolt are a series of lugs and an extractor. The exterior of the bolt has a recess provided therein with an extractor bearing surface that houses the extractor. The forward end of the extractor includes a gripping element, or claw, which catches and holds onto the rim of the case head of an ammunition cartridge.
The extractor rotates about a pin received by both the bolt body and the extractor. Located at the rearward end of the extractor is a spring and internal buffer. The extractor spring and buffer press against the extractor bearing surface thereby resisting rotation of the extractor about its axis and facilitates the extraction of a used ammunition cartridge.
Present on the front face of the bolt is an ejector that is located opposite the side of the front face adjacent the extractor. The ejector consists of a spring-loaded pin which is retained in place on the bolt through the use of a roll pin. The ejector assists in pushing an ammunition cartridge away from the bolt face when the firearm is being fired or otherwise unloaded.
The bolt carrier group is responsible for stripping, chambering, locking, firing, extraction and ejection of ammunition cartridges for the host rifle. The energy to perform these functions is provided in the form of hot, expanding gases which travel through the host firearm's gas tube, through the gas key and into the bolt carrier. A secure union between the gas key and bolt carrier is important to the proper operation of a direct gas operated firearm. Should the gas key become loose or be removed, the associated firearm will not properly function due to resulting gas leakage.
As shown in FIG. 1A, the prior art method of attaching a gas key to the bolt carrier relies on two screws which are torqued and then staked in place.
FIG. 1A illustrates a prior art bolt carrier 60 which uses a separate gas key 61 that has an integral nozzle for communicating with the gas tube of the host rifle. The base of the gas key 61 is secured to the bolt carrier 60 through the use of two retention screws 66. The retention screws are inserted through the openings 62 located on the base of the gas key 61 then threaded into the openings 65 located on the top surface of the bolt carrier 60. This method is deficient as the max torque applied to the screws is not sufficient to prevent the screws 66 from becoming threadedly unsecured due to vibration and the heating/cooling cycle of the host rifle during normal operation. The result is gas leakage which decreases the reliability of the host rifle by causing extraction and feeding related malfunctions.
The retaining pin or cotter pin 64 found in the prior art is retained within an opening 63 that provides no method to orient the pin 64. As a result the pin 64 can be placed either by the user, or through rotation during normal use of the rifle, into a position which orients the thinnest profile of the cotter pin towards the firing pin. This deficiency in the prior art reduces the service life of the cotter pin 64 resulting in several critical issues. The cotter pin can become bent such that maintaining the rifle is difficult since the cotter pin should be removed to service the bolt and bolt carrier properly. Removing a bent cotter pin 64 through the provided opening 63 is difficult, often requiring tools such as pliers to accomplish. Once the cotter pin 64 is removed, the user must be able to reinsert the cotter pin 64 back into the opening 63 of the bolt carrier 60. If the cotter pin 64 is bent, this operation is often virtually impossible. The cotter pin 64 can also break or bend sufficiently thereby rendering the rifle inoperable. The terms “cotter pin” and “retaining pin” are used interchangeably herein.
The prior art bolt has several points of deficiency. First, there are seven bolt lugs placed radially about the forward end of the bolt. These lugs are evenly spaced apart except for the gap created on the exterior of the bolt to accommodate the extractor, which gap is referred to herein as the extractor pocket. When the extractor pocket is machined, a portion of the bolt's face is removed, resulting in the case head of the cartridge not being fully supported.
Second, the lugs located on either side of the extractor pocket are not fully supported, rendering them the weakest lugs on the prior art bolt. As such, these two lugs experience the highest rate of failure. Further, the lugs themselves are machined with sharp edges or geometric corners about their exterior. These geometric corners often accumulate material stress which can result in micro fractures that limit the service life of the bolt.
Third, extraction of a spent cartridge by the extractor, extractor spring and buffer can be disrupted due to a variety of conditions including a fouled barrel chamber, an over pressured gas system, an improperly annealed cartridge rim, as well as others. To compensate for this deficiency, various remedies have been developed to include, for example, the use of o-rings which increase the force the extractor is capable of placing on the rim of an ammunition cartridge.
Fourth and fifth, problems persist with the present method of securing the gas key to the bolt carrier using two screws as described above, and with the method by which the cotter pin that retains the firing pin is able to rotate into a structurally weak position. Finally, there is a deficiency in prior art methods of manufacturing the bolt. It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.